High efficiency magnetron



Sel- 24,1945 I P. L. SPENCER l* 2,408,235 v HIGH EFFICIENCY MAGNETRON vFilfed Dee. 31, 1941 2 Sheets-Sheet l @fw-fw f Patented Sept. 24,` 19462,408,235 HIGH EFFICIENCYMAGNETRON Application December 31, 1941, SerialNo. 425,071

1o claims. (C1. 25o-27.5)

`..This` invention vrelates to a magnetron, and n moreparticularly toone which has a plurality of possible oscillating modes, `each.determined prilInarily by the geometry of theinternal structure of'.the magnetron. A device of this kind is intended to oscillate in apredetermined principal mode so as to generate a predeterminedfrequency. Heretofore the existence of additional modes of oscillationhave introduced serious dificul-ties. Such additional modes Vhave causedspurious oscillations to be generated, thus consuming energy whichreduced the eiciency and effectiveness of the device. f

Anv object of this invention is substantially to eliminate the undesiredcharacter of the additional or spurious modes offoscillation byutilizing them toV reinforce the principal or normal os- `cillator modeof a magnetron.

Another object is to provide means for tuning one mode of oscillationindependent of another so as to bring both modes into synchronism.

A further object is .to increase the eiiiciency and `effectiveness of amagnetron of theforegoing type..

The foregoing and other objects of this invention willrbe bestunderstood from the following vdescription of an exemplii'lcationthereof, reference being had to .the accompanying drawings, wherein:

Fig. 1 is a transverse section of a magnetron v4This block forms theanode of the magnetron.

iThe' block has hollow end sections which are. covered by caps 2 and 3,likewise of .conductive material such as copper. Between the hollow endsections of the block I is located a central bridging portion 4. Theportion 4 is provided with a central bore 5 within which is supportedsubstantially at the center thereof a Acathode 6 which may be of theindirectly-heated oxide-coated thermionic type. The cathode is supportedby a pair of cathode lead-in conductors 1 and 8 sealed through glassseals 9 and I0 mounted at the outer ends of pipes II and I2 hermeticallyfastened within .the walls of the block I'adjacent the upper and lowerhollow end sections. A plurality of slots I3 extend radially from thecentral bore 5,

opening I4 rextending through the bridging portion 4. In this way theanode structure is provided wth a plurality of wedge-shaped arms I5anode sections with the cathode 6.

2 1 .Y to r22, inclusive, the faces of which cooperate as `Whenfsuch amagnetron isy placedrbetween suitable,magneticfpoles -23 and 24 tocreate a longitudinalmagneticfield and the device is energized,oscillations are set up. These oscillations maybe led out from the tubeby means of a cou-A mounted at theV outer end of a pipe 28 likewisehermetically fastened through the wall of the envelope I. -An additionalconducting pipe,v not shown,v may be electrically connected ,to the pipe28,- and forms with the wire 26 a concentric line through which the highfrequency oscillations generated by the magnetron may be conducted to asuitable utilization circuit. v A

A capacity exists between .the cathode 6 and the face of each of theanodesections I 522.V Also capacitances'exist between the side walls ofeach of the slots I3.' The inner walls of the. openings .I4 constituteinductances. The anode, therefore,

is so designed and spaced relative to the cathode that the inductancesand the ,capacitan-ces. de-

scribed constitutey circuits which are tuned, and thus are resonantat avpredetermined frequency .at which the device is to be operated. Thedevice -is intended tooperate so 4that each b ore I4 andv Yits adjacentarms form a circuit tuned to the frequency.l at which each of the'otherbores I4 fand each of said slots terminates in a rcircular yundesiredspurious modes. i vtroublesome mode is that. in which alternate anodearms form opposite ends of an oscillating circuit extendingaround theback of a pair of openings I4. -As more fully described and claimed inmy copending application, Serial No. 421,145, led- December l, 1941,this spurious oscillating mode can be substantially eliminated byinter.- conneoting the `outer ends of alternate anode arms directly `byrelatively low impedance paths. In the arrangement as shown herein, suchinterconnection is made in somewhat different manner from that shown inmy said copending application. As shown in Fig..1, a conductorr 29,preferably of copper, is fastened to and interconnects the anode arms 2|and I9. Also a simi- .lar conductor 30 interconnects anode arms I6 andi8. vThese two connections are made at one end,

vfor example the upper'end of the magnetron structure.

At the other end of the structure a conductor lfpreferably of copper, isconnected to and interconnects ranode arms I5, I'I and I9, while'asimilar conductor 32 interconnects anode 3 arms 22, 20 and I8. Theconductors 3l and 32 overlap, at yone.sicle of the structure, leavingagap at zthe.: otherisidefof said structure along which the conductor 8may extend. Similarly at the other end of the structure conductors `2Sand 3% leave a gap through which the conductor I may extend. In this waytheseinterconnecting conductors may extend beyond the end of thebridging member 4 without interferingwithiithe lead-in conductors 'land`8, respectively, ;Like;

wise a gap between the other ends of the conductors 29 and 30, as showniniFig. 1,.formszafgap permitting an arm 34, the purpose ofwhichwill bedescribed below, to extend along said gap without interference. As willbe seen most clearly *frm-@Figs 4; the interconnections fdescribefd,above interconnect -al-ter-nate' v:anode yarms ydirectly 'throughrelatively vlow impedance -fcon'ductive \'paths, 'thussubstantially-feliminatingthe spurious 'oscillating-mode describedabove. "'Therefore'f the anode'- 'structure' will#oscillate-Wv'ithj each.boref il 4 'and the adjacenty anode u*armsf'iorminga tuned circuit'-as'` describedAl above. "'fThis Inode A'of' oscilla- 'tion'can :betermed' the""transverse mo'de.

v1`Ons-referringtoFig.y 4lit will be vseen that'a path'A existsifromfthe `uppe1'=en"d ffano'de face v22 -to thelowerf'erid; valongtheconductor' 32 tothe 'loweren'd f-anode face 2U,-an'd thencei'fto'theupper ierdl thereof. `TThis ycircuit contains i an apv-preciableamountof -i-nductanceand'some capacitance. I `have found thatundertpropercondi- 'tionsjthedeviee cani be made" to 'oscillate' ener-Afgeticallya'longfsuch a path. Thus the pathtraced can` be made an.oscillating modefvvhich 'may be termed a longitudinal )mode ofoscillation Similar-"oscillating circuits exist respectivelyfibe- 'tweenanode faces 2 I and' I 9,1"2 0 and "I 8, iiand vI l, llland 16; arid Ilandl`5. 'f It will'be -notedthat 'all 'of' i;he 2'1.bove 'longitudinalioscillating paths are (3f-substantially; theL samellength' andcuring-uration* so that thefrequencies' of oscillations in" this mode*are 'substantially equal. The@ frequency' of these oscillations 'thusproduced is determined primarilyby the-length of: the 'ano'dei-facesf I5422.

The frequencyf these oscillations linl'fhelongimoldes: are'stronglyAenergized and reinforceea'ch u Lother. Intubes which'havebuiltin'accordance -withthis invention,I havefoun'd that the total lengthofeach' longitudinal mode of oscillation is approximately equal toene-halfof `a; VWave length fthe*desiredoscillationsigenerated by themagnetr'on.

"It is often'diiicult,topredeterminethev dimensionsv of'the structureexactly so as to make the longitudinal and oscillatingmodes of exactlythe same frequency. Therefore it isf desirable to providemeans "forbringing these two modes of oscillation 'into exactA` synchronism. Forexample; a tuning arrangement as described andclaimed 'in my copendingapplication," Serial No. 420,558, `filed November" 26; 1941, may beIutilized ingorder 'tovary'theinductance of the `transverseoscillatingmodefor tuningy 'that mode. This tuning may .be carriedV outwithout" substantially affecting the frequency of the longitudinal mode.I prefer,

however. toy accomplish this; independent tuning mode.

by an arrangement as illustrated herein. I have found. that `arconductingbody..heldiadiacent the anode; arms I5-22 affects the:icapacity of the circuit involved in the transverse oscillating Varyingthe position of this conducting body will vary this capacity Whileaiecting the .constants-ofthe longitudinal mode in a very much lesserdegree. For the purposes of this device,

thegeffectj of ,this variation on the longitudinal .modelmay'beconsidered as substantially zero.

In order to produce this type of tuning, a light adjacent the anode armsI5-22 at one side of the structure. The ring 33 is split adjacent theleadin conductor i so as to leave a gap permittingadjfjustrnent o'f'the#ring 33f 'in Aa Lvertical*direction :withouty 'inter-ferenceL byg'said' conductor I'L V"The ring-33 may besuppytedsby aasupportingarm.which is bent' hfmg'h"S'u'bsiantiallyl might angie. and extends toy an'disfsupportedbyanutt'. *The nut T35 isVV carriedatthe outer' end dapipe^^36 likewise hermeticallyf sealed through Y ther Wall of theenvelope l. The pipe 36'- isprovidedrwith'a thinned section 31.

"When itis desired to adjust' thepositioniof 'the ring 33' relativelytof the anodel armsfa to'ol 'may be applied to the' nut35 so as4 totwistthe thinned section 31. This twistingfis' suicienttolgive `apermanent setto the'section" '31' to' Whatever 'position the nuty 35*vis turned. Inf thistway" the" ring 33 can be' heldin-'any-fdenitedesired'position relative to the anode'arms within the`tuning limits of the device, rThefrequency of 4the'trans- Verseoscillating `Inode can 'betuned'so'as to bring it into exactsynchronismJ with-the 'freabove,,a"verysremarkable"increase in ,theeiliciency of the'device results. "I'have"fc,und, for example, that theuseful oscillatory powerin a deviceofthis-kindA canreadilyl be Ymade ofv"the orderY of ,sixty per cent.' of the'total'en'ergy' input 'to thetube. lThis is anv extraordinarily high eiiiciency ascomparedwith'those.efciences heretofore 'obtainable in; devicesofthiskind.

Qf courseltit' is to4 be .understood that thislinvention ',is not`l'limited' to the'. particular .details `asfdescribed above as'many.equivalents, will suggest themselves .to those 'skilled' inlthe art.LFor "example, other anode congurations ,couldlbe utilized inpvvhich aplurality. of oscillating modes might Vbeposs'ible. ln. each instance atuning of .various oscillatingmodes into .synchronism with eachother ,byany suitable tuning .means will result in relatively/highefficiencyifsthe principles of myinventionA are followed.

YWhat is claimed is:

l. vAn electron'discharge device Vcomprising. an ,electrode structureincluding Aacathode andn an anode, .said electrode... structurelhaving.a cong- .uration constituting capacitance and. inductance elementsforming. circuits .whichare adapted ,to .have .osc'zillationssetY uprrtherein.. saidoscillations being .all of the ,.same frequency,V a,plurality of predetermined points y on 4.said velectrode,,structureatwhichin-phase voltageloops of saidoscillations occur, andrelatiizelylow .impedance .means directly interconnectingsaid .pointsand formingwith portions of said electrode structure an additional oscillatingcircuit, the `frequency of said last-named oscillating circuit beingsubstantially equal to the frequency of said firstnamed oscillatingcircuits.

2. An electron discharge device comprising a cathode and an anode, saidanode having a plurality of electron-receiving portions adjacent saidcathode, and a plurality of grooved portions spaced from saidelectron-receiving portions forming a plurality of inductances whichtogether with the interelectrode capacitances constitute a plurality oftuned circuits adapted to oscillate at a first frequency, relatively lowimpedance means directly interconnecting alternate electron-receivingportions, each pair of electron-receiving portions ,thus interconnectedforming a tuned circuit adapted to oscillate at a second frequency, saidsecond frequency being substantially equal to said first frequency.

3. An electron discharge device comprising a cathode and an anode, saidanode having a plurality of electron-receiving portions adjacent saidcathode, and a plurality of grooved portions spaced from saidelectron-receiving portions forming a plurality of inductances whichtogether with the interelectrode capacitances constitute a plurality oftuned circuits adapted to oscillate at a first frequency, relatively lowimpedance means directly interconnecting alternate electron-receivingportions, each pair of 4. A magnetron comprising an electrode structureincluding a cathode and an anode, means for producing a magnetic eldabout said cathode, said electrode structure having a configurationconstituting capacitance and inductance elements forming circuits whichare adapted to have oscillations set up therein, said oscillations beingall of the same frequency, a plurality of predetermined points4 on saidelectrode structure at which in-phase voltage loops of said oscillationsoccur, and relatively low impedance means directly interconnecting saidpoints and forming with portions of said electrode structure anadditional oscillating circuit, the frequency of said last-namedoscillating circuit being substantially equal to the frequency of saidfirstnamed oscillating circuit.

5. A magnetron comprising acathode and an anode, means for producing amagnetic field about said cathode, said anode having a plurality ofelectron-receiving portions adjacent said cathode, and a plurality ofgrooved portions spaced from said electron-receiving portions forming aplurality o-f inductances which together with the interelectrodecapacitances constitute a plurality of tuned circuits adapted tooscillate at a first frequency, relatively low impedance means directlyinterconnecting alternate electron-receiving portions, each pair o-felectron-receiving portions thus interconnected forming a tuned circuitadapted to oscillate at a second frequency, said second frequency beingsubstantially equal to said first frequency.

6. An electron discharge device kcomprising a cathode and an anode,saidv anode having a plurality of electron-receiving portions adjacentsaid cathode and circularly disposed around said cathode, and a.plurality of grooved portions spaced from said electron-receivingportions forming a plurality of inductances which together with theinterelectrode capacitances constitute a plurality of tuned circuitsadapted to oscillate in a first oscillating mode, a lead-in conductorfor said cathode lying in a plane extending substantially between twoadjacent electron-receiving portions, yalternate electron-receivingportions` being directly interconnected by relatively low impedancemeans, said loW impedance means directly connecting each of saidelectron-receiving portions to the two alternate electron-receivingportions With the exception of the two pairs of electron-receivingportions lying on opposite sides of said plane, each of said latterelectronreceiving portions being directly connected by said lowimpedance means only to the alternate electron-receiving portion lyingon the same side of said plane, whereby none of said 10W impedance meanscross said plane.

7. An electron discharge device comprising a sealed envelope containingan elongated cathi ode, an anode structure having adjacent anodeelements defining a transverse cavity resonator, the free ends of saidanode arms constituting electron-receiving portions, an adjustabletuning element Within said envelope, said tuning element comprising aconductive member supported adjacent said free ends of said anode arms,and means connected to said tuning element for adjusting the position ofsaid element toward and away from said cavity resonator.

8. A magnetron comprising a cathode surrounded by an anode block, saidblock having a central cathode space and interconnecting spaces formingcoupled cavity resonators, said block also having a pair of anode armsforming opposite sides of each of said cavity resonators, the free endsof said anode arms constituting electron-receiving portions, anadjustable tuning element within said envelope, said tuning elementcomprising a conductive member supported adjacent said free ends of saidanode arms, and means connected to said tuning element for adjusting theposition of said element toward and away from said cavity resonator.

9. An electron discharge device comprising a sealed envelope containingan elongated cathode, an anode structure having adjacent anode elementsdefining a transverse cavity resonator, the free ends of said anode armsconstituting electron-receiving portions, an adjustable tuning e1- ementwithin said envelope, said tuning element comprising a conductive membersupported adjacent said free ends of said anode arms, and means operableexternally of said envelope and connected to said tuning element foradjusting the position of said element toward and away from said cavityresonator.

10. A magnetron comprising a cathode sursaid cavity resonator.

PERCY L. SPENCER!

